adding layers in ggplot2 (data and code included)

Here is some sample data:

mydata <- read.table(textConnection("Est Group    Tri
       0        0 4.639644
       1        0 4.579189
       2        0 4.590714
       0        1 4.443696
       1        1 4.588243
       2        1 4.650505
       0        2 4.296608
       1        2 4.826036
       2        2 4.765386"),header=TRUE);
  closeAllConnections();

I can form two plots, scatter and  lines, as follows:

p <- ggplot(mydata, aes(x=Est, y=Tri))
p + geom_point(aes(colour=factor(Group),shape=factor(Group)))

and

p+ geom_smooth(aes(group=factor(Group),color=factor(Group)),method=lm,se=F).

However, I am unable to have the plots together.

I obtain the following error:

  

p + geom_point(aes(colour=factor(Group),shape=factor(Group)))+geom_smooth(aes(group=factor(Group),color=factor(Group)),method=lm,se=F)
    

Error in `[.data.frame`(df, , var) : undefined columns selected

Thanks,

Juliet